Gene Mutations and Autism Risk: A Link?
In any discussion about how common autism has become — 1 in 88 children in the U.S. are now diagnosed with the neurodevelopmental disorder — the question of “why” inevitably rises. Many autism experts emphasize how the expanded DSM criteria for autism spectrum disorders have greatly contributed to the rise in diagnoses. Scientists keep looking for possible environmental and genetic factors. Three new studies have just been published in the journal Nature about several gene mutations that, the researchers says, are linked to a higher risk of autism.
The genes in question are de novo mutations — spontaneous copy number mutations in the DNA. Previous studies have shown that such gene mutations occur more often in cases of sporadic autism rather than they do in familial (heritable) cases or than in children who do not have an autism spectrum disorder.
In the three new Nature studies, scientists examined genetic material from blood samples from families in which the parents had “no signs of autism” and an autistic child.
(1) A study under Dr. Matthew W. State, a professor of genetics and child psychiatry at Yale University, looked for de novo mutations in samples from 200 people with an ASD diagnosis and in their parents and siblings who did not have such a diagnosis. Two unrelated autistic children were found to have de novo mutations in the same gene.
(2) A study of 209 families under Dr. Evan E. Eichler, a professor of genome sciences at the University of Washington in Seattle, found a de novo gene mutation in a different gene suspected of a possible link to autism risk. One autistic child in Dr. State’s study was found to have a de novo mutation in the very same gene.
(3) A third study under Mark J. Daly of Harvard University analysed the de novo gene mutations from the other studies as well as a third gene and found that, as noted in The New York Times, “kids with autism have a slightly higher rate, on average, and the effects are more severe.”
One caveat regarding de novo mutations and “sporadic autism”: The autistic children in the three new studies are described as having no family members with an autism diagnosis. However, it is not unusual for parents of autistic children to see some aspects of their child — a tendency to be obsessive-compulsive, difficulties with attention, perhaps — in themselves; some parents have even been diagnosed with Asperger’s after their child received an ASD diagnosis. If the expanded criteria for autism were applied to parents and siblings, might they not be found to have some “autistic traits”?
Parental Age and Autism Risk
All three studies also noted that, the older parents are, the greater the risk for giving birth to a child at risk for an autism diagnosis. Earlier studies have also suggested that older parents (both male and female) are more at risk for having an autistic child.
There are some caveats about correlating parental age and autism risk. For instance, parents who are “different” in some way, having ADHD or Asperger’s Syndrome, perhaps, may be more likely to have children later, due to their own challenges with relationships and social interactions.
So What Do These Studies Tell Us?
Currently autism is diagnosed by the observation of clinicians and psychologists, who examine a child to see if she or he has sufficient quantities of symptoms to qualify for an ASD diagnosis. In other words, diagnosing autism retains an element of subjectivity. The still-changing and evolving criteria for autism add to the challenge and, too, the confusion. Researchers have been hopeful that genetic studies might point to a possible biomarker for autism.
Jonathan Sebat, a professor of psychiatry and cellular and molecular medicine at the University of California, San Diego who was not involved in the three new studies, describes the studies not as a “breakthrough, because we knew this was coming” but as a “turning point.” Sebat said that “in the next year or two” we can likely expect to find “20, 30, maybe more such mutations.”
Like previous genetic studies about autism, the new studies have found rare genetic mutations in only a very few individuals vs. some “autism gene” in many individuals. Developing therapies from the new studies’ findings is a long way off. What the new studies, and future studies like them, may end up telling us is that “what is known generally as autism may represent a broad category of related but biologically distinct conditions.” Finding a biomarker that would definitely say “this child is autistic” remains elusive.
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